

const PENDING = 'pending';//等待
const FULFILLED = 'fulfilled';//成功
const REJECTED = 'rejected';//失败

class MyPromise {
    constructor(executor) {
        try {
            executor(this.resolve, this.reject)
        } catch (e) {
            this.reject(e)
        }

    }
    // promise 状态
    status = PENDING
    // 成功之后的值
    value = undefined;
    // 失败之后的原因
    reason = undefined;
    // 成功回调
    successCallback = []
    // 失败回调
    failCallback = []
    resolve = value => {
        // 如果状态不是等待，阻止程序继续执行
        if (this.status !== PENDING) return;
        // 更改状态为成功
        this.status = FULFILLED;
        // 保存成功后的值
        this.value = value
        // 判断成功回调是否存在 如果存在 调用
        // this.successCallback && this.successCallback(this.value)
        while (this.successCallback.length) this.successCallback.shift()()

        // while(this.successCallback.length) this.successCallback.shift()(this.value)
    }
    reject = reason => {
        // 如果状态不是等待，阻止程序继续执行
        if (this.status !== PENDING) return;
        // 更改状态为失败
        this.status = REJECTED
        // 保存失败之后的原因
        this.reason = reason
        // 判断失败回调是否存在 如果存在 调用
        // this.failCallback && this.failCallback(this.reason)
        // while(this.failCallback.length) this.failCallback.shift()(this.reason)
        while (this.failCallback.length) this.failCallback.shift()()

    }
    then(successCallback, failCallback) {
        successCallback = successCallback ? successCallback : value => value
        failCallback = failCallback ? failCallback : reason => { throw reason }
        let promise2 = new MyPromise((resolve, reject) => {
            // 判断状态
            if (this.status === FULFILLED) {
                // 由于要返回promise2本身，需要代码执行完成，不然会报错找不到，添加到宏任务中
                setTimeout(() => {
                    try {
                        let x = successCallback(this.value)
                        // 判断x 的值是普通之还是promise对象
                        // 如果是普通值 直接调用resolve
                        // 如果是promise对象 查看promise对象返回的结果
                        // 再根据promise对象返回的结果 决定调用resolve还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }

                }, 0)
                //    resolve(x)
            } else if (this.status === REJECTED) {
                setTimeout(() => {
                    try {
                        let x = failCallback(this.reason);
                        // 判断x 的值是普通之还是promise对象
                        // 如果是普通值 直接调用resolve
                        // 如果是promise对象 查看promise对象返回的结果
                        // 再根据promise对象返回的结果 决定调用resolve还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }
                }, 0)
            } else {
                //等待
                // 将成功，失败回调存储起来
                // this.successCallback.push(successCallback) 
                // this.failCallback.push(failCallback) 
                this.successCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = successCallback(this.value)
                            // 判断x 的值是普通之还是promise对象
                            // 如果是普通值 直接调用resolve
                            // 如果是promise对象 查看promise对象返回的结果
                            // 再根据promise对象返回的结果 决定调用resolve还是调用reject
                            resolvePromise(promise2, x, resolve, reject)
                        } catch (e) {
                            reject(e)
                        }

                    }, 0)
                })
                this.failCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = failCallback(this.reason);
                            // 判断x 的值是普通之还是promise对象
                            // 如果是普通值 直接调用resolve
                            // 如果是promise对象 查看promise对象返回的结果
                            // 再根据promise对象返回的结果 决定调用resolve还是调用reject
                            resolvePromise(promise2, x, resolve, reject)
                        } catch (e) {
                            reject(e)
                        }
                    }, 0)
                })
            }
        })

        return promise2
    }
    static all(array) {
        let result = [];
        let index = 0;
        return new MyPromise((resolve, reject) => {
            function addData(key, value) {
                result[key] = value;
                index++;
                if (index === array.length) {
                    resolve(result);
                }
            }
            for (let i = 0; i < array.length; i++) {
                let current = array[i];
                if (current instanceof MyPromise) {
                    // promise 对象
                    current.then(value => addData(i, value), reason => reject(reason))
                } else {
                    // 普通值
                    addData(i, array[i]);
                }
            }
        })
    }
    static resolve(value) {
        if (value instanceof MyPromise) return value;
        return new MyPromise(resolve => resolve(value));
    }
    // 成功失败都走
    finally(callback) {
        return this.then(value => {
            return MyPromise.resolve(callback()).then(() => value);
        }, reason => {
            return MyPromise.resolve(callback()).then(() => { throw reason })
        })
    }
    catch(failCallback) {
        return this.then(undefined, failCallback)
    }

}
function resolvePromise(promise2, x, resolve, reject) {
    // 解析其是否同一个promise对象（自己调用自己）
    if (promise2 === x) {
      
        return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
    }
    if (x instanceof MyPromise) {
        // promise对象
        // x.then(value=>resolve(value),reason =>reject(reason))
        x.then(resolve, reject)
    } else {
        // 普通值
        resolve(x)
    }
}
module.exports = MyPromise